Impact of Cumulus Convection Parameterization on 2022 Hurricane IAN and Earl Forecasts in the NOAA Global Forecast System

The NOAA Global Forecast System (GFS) had relatively large track biases in forecasting certain hurricanes during the 2022 hurricane season. In order to better understand the hurricane forecast behaviors in the GFS, we selected Hurricane IAN and Hurricane EARL for our investigation. There is a large westward track bias for hurricane IAN, and large eastward track bias for Hurricane EARL. A series of simulations were carried out using different cumulus convection parameterization schemes in the GFS. Results show that cumulus convection parameterization has a large impact on both hurricane track and intensity forecasts. Analyses from the simulations indicate that different cumulus convection parameterization not only changes the large scale flow pattern, but also changes the hurricane internal structures (and hurricane intensity) in the GFS. Compared to the GFS and ECMWF analyses, the forecast easterly wind in the tropics and westerly wind near the Westerly Jet Stream were too strong, which are the primary causes for the large cross-track errors found in the operational GFS forecasts.